1. Field of the Invention
The present invention relates to a wafer processing system that processes wafers which have been formed by cutting silicon ingots or through other methods. More particularly, the present invention pertains to a wafer processing system that enables various processes such as the washing of semiconductor wafers to be performed efficiently.
2. Description of the Related Art
Semiconductor wafers are generally formed by cutting apart silicon ingots at predetermined intervals using a wire saw or the like. An example of the cutting method will now be described.
As shown in FIG. 18(a), a silicon ingot, or cylindrical workpiece 22 has an adhering plate 23 adhered to its upper surface. The adhering plate 23 includes a carbon layer 23a and an insulating layer 23b. An adhesive agent 23c is applied between the adhering plate 23 and the workpiece 22. As shown in FIG. 19, the adhering plate 23 is employed to couple the workpiece 22 to a holding mechanism 17 of a wire saw 16. The wire saw 16 includes a plurality of rollers 18, a wire 19 wound spirally around the rollers 18 with a predetermined pitch between each winding, and supply pipes 15 through which slurry that contains abrasive grains is supplied to the wire 19. As shown in FIGS. 18(b) and 19, the wire 19 is drawn in either a single direction or two directions while the slurry, which includes abrasive grains, is supplied to the wire 19. In this state, the workpiece 22 is pressed against the wire 19. The wire saw 16 thus cuts apart the workpiece 22 and produces a plurality of wafers 22a simultaneously.
The adhering plate 23 remains adhered to the wafers 22a after the cutting. Then, the cut wafers 22a are dipped into a dissolving liquid or heated water that contains an organic solvent. The liquid softens the adhering agent between the adhering plate 23 and the wafers 22a and thus removes the wafers 22a from the plate 23.
The wafers 22a removed from the adhering plate 23 produce a stack of wafers 22a. Considering the subsequent processing steps, it is required that each wafer 22a be separated from the other wafers 22a. Thus, a separating apparatus is used to separate each wafer 22a. Each separated wafer 22a is retained in a retaining container such as a cassette.
Cutting chips and slurry that include abrasive grains are adhered to the wafers 22a when they are cut apart. Hence, the wafers 22a retained in the container are washed by a washing apparatus.
However, washing the wafers 22a retained in the container is inefficient and it is difficult to ensure removal of the cutting chips and other foreign material from the surface of the wafers 22a. In addition, during the step in which the cut wafers 22a are retained in the container, there is a possibility that the wafers 22a may be damaged by the cutting chips or abrasive grains.
Furthermore, a long period of time is required to allow the dissolving liquid or heated water permeate into the narrow space between adjacent wafers 22a. As a result, it takes a long time to sufficiently soften the adhesive agent 23c applied between the adhering plate 23 and the wafers 22a. This lengthens the time required to remove the wafers 22a from the adhering plate 23.
It is difficult to separate the wafers 22a one at a time since they are extremely thin and break easily. Japanese Unexamined Patent Publication Nos. 4-3744 and 5-63058 describe separating apparatuses that utilize water streams.
Japanese Unexamined Patent Publication No. 4-3744 describes an apparatus that arranges a plurality of stacked wafers within a liquid. Each wafer is separated from the stack through suction and injection of the liquid. However, the suction and injection of the liquid results in the structure of the apparatus becoming complicated. Furthermore, it is difficult to accurately control the movement of the wafers in the liquid. When suction and injection of the liquid is not carried out accurately, an unexpected stream of the liquid may be produced. As a result, it becomes difficult to separate each wafer 22a without inflicting any damage. Accordingly, it is extremely burdensome to control the suction and injection of the liquid.
Japanese Unexamined Patent Publication No. 5-63058 describes an apparatus that separates a wafer arranged at the uppermost position of the wafer stack by injecting a liquid toward the wafer. This separates the uppermost wafer in a predetermined direction. However, it is difficult to ensure separation of each wafer merely be injecting liquid.